Results: Researchers at the University of California, Los Angeles, have used a complex of molecules to create nanoscale valves for porous silica nanoparticles. The researchers demonstrated that the molecules can seal a fluorescent dye inside the nanoparticles. When the pH of water surrounding a particle changes, part of the nanovalve detaches, allowing the dye to escape.

Why it matters: The nanoparticles could eventually be used to deliver drugs to diseased cells within the body, which differ in pH from healthy cells. A diseased cell that ingested a nanoparticle would cause it to release a drug. Such targeted drug delivery could decrease the side effects of existing treatments and allow the use of drugs that would be either ineffective or lethal if delivered throughout the body. Other nanovalves have been made in the past, but they were activated by special solvents and thus wouldn’t work in the body.

Methods: The researchers made porous silica nanoparticles and chemically treated them, attaching linker mole­cules to them. After loading the nanoparticles with a fluorescent dye, they sealed the pores by binding molecular complexes to the linkers. Then they placed the nanoparticles in water, raised the pH by adding sodium hydroxide, and monitored the release of the dye.

Next steps: The current system works only at harsh pH levels. The researchers are working to develop a system that responds to the gentler pH levels of diseased cells within the body, a crucial modification if the system is to be used for actual drug delivery.